Field of the Invention
The present invention relates to honeycomb filters. Specifically the present invention relates to a honeycomb filter having excellent temperature-rising property and capable of increasing the deposition limit of particulate matter, such as soot, during the regeneration operation to burn the soot trapped with the filer for removal.
Description of the Related Art
Internal combustion engines are used as a power source in various industries. Exhaust gas emitted from an internal combustion engine during fuel burning, however, contains particulate matters, such as soot and ash, together with toxic gas, such as nitrogen oxides. Hereinafter the particulate matters may be called “PM”. “PM” stands for “Particulate Matter”. Regulations on the removal of PM emitted from a diesel engine are becoming stricter worldwide. A honeycomb-structured wall flow type filter, for example, has been used for a filter to remove such PM.
Various types of honeycomb filters have been proposed as the wall-flow type filter, and such a filter includes a honeycomb substrate having a porous partition wall that defines a plurality of cells serving as a through channel of fluid, and a plugging portion disposed at the open ends of the plurality of cells on any one side (see, for example, Patent Documents 1 to 4). Such a honeycomb filter has inflow cells having a plugging portion at their outflow end faces and outflow cells having a plugging portion at their inflow end faces, the inflow cells and the outflow cells being disposed alternately via the partition wall. The porous partition wall serves as a filter to remove PM.
For a long term use of a honeycomb filter, the honeycomb filter has to be regenerated regularly. This is because PM, such as soot, is deposited inside of the honeycomb filter over time, so that the pressure loss of the filter increases gradually. In order to bring back the filtering performance of the honeycomb filter closer to its initial state, PM, such as soot, deposited inside of the honeycomb filter has to be burned with a high-temperature gas for removal. For a smooth regeneration treatment, a honeycomb filter may be loaded with catalyst to burn the soot for removal. For such catalyst, noble metals, such as platinum and palladium, are used. In the following, the operation to burn the soot deposited inside of a honeycomb filter may be called simply “regeneration” or “regeneration operation” of the honeycomb filter. Particularly the operation to increase the temperature of exhaust gas flowing into a honeycomb filter regularly and intentionally for the regeneration may be called “forced regeneration”.                [Patent Document 1] JP-A-2007-209842        [Patent Document 2] JP-A-2012-081415        [Patent Document 3] JP-B-4279497        [Patent Document 4] JP-B-4567674        